Device and method for recovery and reliquefaction of boil-off gas of liquefied natural gas

Abstract

The invention relates to a device for the recovery and reliquefaction of boil-off gas of liquefied natural gas, which comprises a storage tank with a safety valve and a low-temperature pump, wherein a first interface is formed between the storage tank and the safety valve and is connected with a recovery pipe; the low-temperature pump is provided with a second interface; the other end of the recovery pipe is communicated with a recovery compressor; an outlet of the recovery compressor is connected with a cooler, an oil-gas separator and a boil-off gas distributor, and first boil-off gas and second boil-off gas are respectively discharged from the boil-off gas distributor; the first boil-off gas is communicated with a screw expansion machine and enters a heat exchanger and a second screw compressor; the second boil-off gas is connected with the second interface of the low-temperature pump by the heat exchanger, a throttling valve and a gas-liquid separator; and the liquefied natural gas enters the storage tank. The device has the advantages that by using a screw expansion-compressor set refrigerating reliquefaction method of recovering the boil-off gas directly by the screw compressors and taking the boil-off gas as a refrigerant directly, system flow equipment is simplified, energy waste is avoided, and peripheral environmental pollution and potential safety hazards are avoided, so obvious economic and social benefits are created; and a system runs automatically, continuously and circularly, and has the excellent running work condition and high using efficiency and runningreliability.

Description

technical field [0001] The present invention relates to the technical field of cryogenic liquefied gas storage and transportation; specifically refers to a device and method for recovery of liquefied natural gas (LNG) boil-off gas (BOG) in a storage tank and its reliquefaction; it can be widely used in various types of The recovery and reliquefaction of boil-off gas in liquefied natural gas storage equipment. Background technique [0002] Liquefied natural gas (LNG) is currently an ideal clean fuel; the promotion and application of LNG is a very important task to improve energy efficiency and social benefits. [0003] The liquefied natural gas (LNG) is a low-temperature liquid formed by cooling natural gas to the dew point temperature after purification. The temperature at normal pressure is -163°C; Shipping and handling. [0004] Since the ambient temperature of the storage tank is usually higher than the temperature of the liquefied natural gas in the storage tank, under...

AI Technical Summary

Problems solved by technology

[0007] The daily vaporization rate of boil-off gas designed for existing liquefied natural gas storage tanks is generally 0.05% of the total volume; the factors that produce boil-off gas in the storage tank are: first, loading and unloading operations will produce a large amount of boil-off gas; , the cold cycle facility of the storage tank will also produce the boil-off gas with heat input; thirdly, the high-pressure pump and pipeline also have heat input, and will also produce the boil-off gas; The tumbling caused by stratification will also bring violent evaporation, and thus generate the boil-off gas; in summary, these boil-off gases are directly released into the atmosphere, or burned through the flare system, which not only wastes a lot of energy but also Cause direct economic losses, but also cause pollution to the surrounding environment, and cause hidden dangers to the safety of the surrounding environment

[0008] At present, the traditional natural gas liquefaction adopts low-temperature liquefaction method, including cascade liquefaction process, mixed refrigerant liquefaction process and liquefaction process with expander, etc. This method has a complex process system and is suitable for large-scale production. Each process A liquefied natural gas plant must be established; yet, for the liquefaction of boil-off gas in the storage tank and storage tank area, there are also corresponding recovery and re-liquefaction devices and methods for the boil-off gas at present

Images